Can a Lean-To Conservatory Have a Tiled Roof?

Every tile and slate has a lowest workable pitch, the slope below which wind can drive rain up under the laps. A lean-to roof is often shallow, because it was built to carry polycarbonate or glass, which can be laid almost flat.

What pitch do tiles need?

Marley lists minimum pitches that run from 12.5 degrees for its Mendip 12.5 concrete tile and 15 degrees for the Mendip and Wessex tiles, up to 22.5 degrees for the smooth Double Roman and 35 degrees for the concrete plain tile. Its Lincoln clay pantile is listed at 15 degrees. For natural slate, Cupa says BS 5534 indicates 20 degrees. The maker's published sheet for the exact tile is the only safe guide, because the figure changes with the profile and with the exposure.

Measure your own pitch before falling for a tile. A lean-to under 15 degrees rules out most tiles, and a solid roof of another kind, such as a lightweight system or a membrane, may suit it better. A spirit level and a tape measure are enough for a rough reading. Exposure shifts the answer too. A site open to wind asks more of the laps than a sheltered back garden, so a pitch that only just passes on paper deserves a second look.

A conservatory frame was designed for the roof it came with. Plain concrete or clay tiles weigh far more than polycarbonate, and the walls, the plate and the glazing bars were not sized for that.

Can a lean-to take the weight?

Sometimes with strengthening, sometimes not. The Planning Portal recommends a structural check before work begins, and says that a new covering making the roof at least 15 per cent heavier needs Building Regulations approval. Where the old roof was glazed, a tile roof is certain to go past that. Ask who is signing off the weight. A roofer, an engineer and building control each look at it differently, and you want one of them to put the answer in writing before the old roof comes off.

That is why lean-tos often go to lightweight tiled systems, which use tile-effect panels or thin tiles on a lighter frame. Our answer on lightweight conservatory roof tiles explains what those are and why weight matters. The wider guide to a tiled conservatory roof covers the other options.

A new tiled roof changes the building, and the paperwork follows the type of change.

Do you need Building Regulations approval?

The Planning Portal treats a replacement conservatory roof as work that the Building Regulations cover. Ask Somerset Building Control, on 0300 303 7790, how they want the work notified. A tiled roof also raises thermal and ventilation questions that a glazed one never did. Somerset Building Control gives an expected reply to a full plans application within 10 working days and a decision normally inside 5 weeks, so allow for that wait.

Do you need planning permission?

Re-roofing a house with a new covering is normally permitted development under Class C, but how a conservatory is treated depends on the building and its position. For a listed building, or any house within a conservation area, ask Somerset Council's planning team before ordering anything. The Exmoor National Park Authority, not Somerset Council, handles planning for addresses inside the Park.

The structure goes on first: rafters or a lightweight frame sloping from the wall plate down to the eaves beam. On top comes the underlay, a sheet that acts as the second line of defence if water gets past the tiles, then the battens, the slim timber laths the tiles hook onto, and finally the covering.

What happens at the wall?

The top of the roof meets the house wall, and that junction is sealed with lead flashing set into a chase. Our answer on how a conservatory roof is sealed to the house explains the detail. At the lower edge, a gutter and fascia finish the job, and no ridge is needed because a lean-to has only one slope.

Inside, the ceiling is plasterboard under the rafters, with insulation and a vapour layer above it. The detail must match the maker's system, which is why our advice follows the survey of your frame and pitch. We give one written price, take pictures of what we find and explain each day of the work. For the full list of choices, see our conservatory roofs page, and start with the measured pitch. Tell us the pitch and the width of the wall it leans against, and we can say whether tiles are realistic before the survey.